Silicon Negative Electrode Particle Control for Battery Swelling
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Solution Overview
Problem
Existing lithium secondary batteries using silicon-based negative electrodes face challenges with cell swelling, cell breathing, and rapid performance degradation due to uneven lithium ion intercalation and deintercalation, leading to reduced capacity and safety issues.
Innovation Solution
The lithium secondary battery design includes a silicon-based negative electrode with controlled crystal grain size and average particle diameter, optimizing cell swelling and breathing values within specific ranges, using a negative electrode active material layer with a silicon-based active material, a conductive material, and a binder to ensure uniform lithium ion diffusion and reduce electrolyte consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a silicon-based negative electrode is used to increase capacity, then energy density is improved, but cell swelling and performance degradation occur due to volume expansion during lithium ion intercalation
Solution Approach 1:
The silicon-based negative electrode is divided into fine particles with an average particle diameter of 1 μm to 7 μm. This segmentation reduces the volume expansion stress within each particle and prevents cracking, thereby maintaining service life while utilizing the high capacity of silicon
Solution Approach 2:
A carbon coating layer is applied only on the surface of the silicon-based active material particles. This local modification provides mechanical strength and prevents electrolyte penetration into the interior, suppressing volume expansion effects at the particle level while preserving the high capacity of silicon
2Speed
If the negative electrode active material layer is made thin to reduce lithium diffusion distance, then charging rate is improved, but capacity is reduced
Solution Approach 1:
The average particle diameter of the silicon-based active material is optimized to 1 μm to 7 μm, and the thickness of the negative electrode active material layer is controlled at 20 μm to 500 μm. These parameter optimizations balance the lithium diffusion distance with the total capacity, achieving both rapid charging and high capacity
3Quantity of substance
If silicon content is increased to improve energy density, then capacity increases, but gas generation and stability problems occur
Solution Approach 1:
A carbon coating layer is applied on the surface of silicon-based active material particles to locally suppress electrolyte decomposition and gas generation reactions, enabling high silicon content (70-100 wt%) while minimizing harmful gas evolution
Solution Approach 2:
The carbon coating layer, while adding a small amount of mass, prevents the harmful gas generation reactions between silicon and electrolyte, thereby converting a potential disadvantage into a benefit by enabling higher silicon content and improved energy density
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The optimized design achieves high capacity, high energy density, and improved service life by controlling cell swelling and breathing, ensuring uniform reactions and reducing gas generation, thereby enhancing the battery's performance and safety.
Implementation Method 1
During charging, the lithium ions intercalated to the positive electrode migrate to the negative electrode through the electrolyte solution. During discharging, the lithium ions migrate back to the positive electrode from the negative electrode.
Implementation Method 2
During charging, lithium migrating from the positive electrode to the negative electrode reacts with the electrolyte solution to form a kind of passivation film, that is, a solid electrolyte interface (SEI), on a surface of the negative electrode. The SEI inhibits transport of electrons required for the reaction of the negative electrode with the electrolyte solution to prevent decomposition of the electrolyte
Implementation Method 3
to achieve high output by reducing internal resistance by forming a carbon-coated layer on a surface of the negative electrode active material layer to increase conductivity
Data Source
Figure 1~2
AI summary
The present application relates to a lithium secondary battery.